The use of liquified gases and supercritical fluids to carry out extractions at high elevated pressure has been described in the prior art. Such prior art processes involve the use of liquified gases or supercritical fluids at pressures in excess of 3,000 to 5,000 psi, although in some cases the recommended pressures exceed 10,000 psi.
Processes for extractions run at extremely high pressures are described in the following U.S. Pat. Nos.: 4,156,688; 4,328,255; 4,466,923; 4,493,854; 4,495,207; and 4,683,063.
Generally speaking, these prior art processes separate the extracted material from the residual solids by an elution or dilution process, wherein the supercritical fluids are pumped through the material to be extracted over a period of time, and as the extracting fluid is pumped through the solids, the level of extractable liquid in the solids is gradually reduced.